1. Field of the Invention
The present invention relates in general to automotive automatic transmissions of a so-called shift-by-wire type wherein a range change of the transmission is carried out by an actuator that is controlled in accordance with a range selection command signal issued from a range selector manually actuated by a driver, and the more particularly to a range selection control device that carries out the above-mentioned automatic range change of the transmission. More specifically, the present invention relates to the range selection control devices of a type that can cope with such a difficult case wherein the range selector fails to issue the command signal.
2. Description of the Related Art
In automatic transmissions having a continuously variable transmission unit installed therein, there is arranged a link mechanism between a shift lever that is manipulated by a driver and a manual valve that is installed in a hydraulic control circuit of the transmission. That is, when, upon need of a speed change, the driver shifts the shift lever to a desired range, the manual valve is shifted to a position to induce a desired operation range of the transmission that corresponds to the range desired by the driver.
In the field of the automatic transmissions, a so-called shift-by-wire type has been proposed and put into practical use for allowing the transmission to exhibit a much improved performance. That is, in the shift-by-wire type transmissions, the range section is electronically carried out.
One of the automatic transmissions of such shift-by-wire type is shown in Japanese Laid-open Patent Application (Tokkaihei) 5-203042, which comprises a range selection switch (or range selector) that issues a corresponding range selection command signal when a driver shifts the shift lever to P(parking)-range, R(reverse)-range, N(neutral)-range, or D(drive)-range, and an electric motor (or actuator) that moves the manual valve to a corresponding position upon receiving the range selection command signal from the range selection switch.